Editor, Alex Bell, focuses on the unique reproductive traits and care requirements of the rare and fascinating Borneo redline halfbeak, a lesser-known species of halfbeak that stands out due to its egg-laying behaviour, unlike its viviparous relatives.
Like many aquarists, my exposure to halfbeaks has been limited. For years, my only real experience was with the wrestling halfbeak (Dermogenys pusilla) – a hardy, adaptable species found in everything from stagnant freshwater ditches to brackish mangroves. While still uncommon, it’s at least a fish you’ll occasionally spot in shops or fellow hobbyists’ tanks.
This guide, however, focuses on a far rarer and more specialised species: the Borneo redline halfbeak (Hemirhamphodon tengah). Unlike its more adaptable relatives, this fish demands specific conditions – and rewards the dedicated aquarist with truly unique behaviour and biology.
Tank Size and Setup for Halfbeaks
Despite reaching only around 5cm in length, H. tengah requires a tank with a large surface area rather than sheer volume.
All halfbeaks are obligate surface dwellers, rarely straying more than a few inches below the waterline. In the wild, they rely on floating vegetation for protection. Without it, they’re vulnerable to predators from above and below.
In captivity, this instinct creates a problem.
When startled, halfbeaks dart rapidly across the surface. In smaller tanks, this often results in collisions with the glass—frequently damaging their delicate, elongated lower jaw.
Recommended tank size:
- Minimum: 75cm (30") length
- Ideal: 100x40cm (39x16") footprint or larger
During a period in a smaller 60x30cm (24x12") tank, I observed frequent collisions, reinforcing just how important space is for this species.
Reducing Stress and Injury
If space is limited, there are ways to minimise risk:
- Dense planting along the sides and back (e.g. tall species like Cryptocoryne balansae)
- Darkened tank walls (paint or background) to improve visibility of boundaries
- Floating plants provide cover and reduce stress
These measures help reduce both the frequency and intensity of panic responses.
Preventing Jumping
Like many nervous surface fish, Borneo redline halfbeaks are prone to jumping.
To prevent escapes:
- Use a tight-fitting lid or cover glass
- Maintain dense surface vegetation
- Avoid sudden lighting changes
If possible, use lighting systems with gradual sunrise/sunset transitions, as sudden changes are a major trigger for darting and jumping behaviour.
Borneo Halfbeak Aquarium Care
As always when considering a new species, you need to ascertain if you can provide the correct water chemistry for them. Living in the peat swamps of Borneo, it is a safe assumption that a soft, acidic environment would be needed. A pH below 6.5 will be acceptable but for most aquarists that means the use of reverse osmosis water will be required—this will also keep the carbonate hardness low which is also a necessity.
Water Parameters and Conditions
Originating from theblackwater peat swamps of Borneo, this species requires soft, acidic conditions.
Ideal water parameters:
- pH: 5.5–6.5
- Hardness: Very low (0–8°H)
- Temperature: 25–28°C
For most aquarists, achieving these conditions will require reverse osmosis (RO) water.
Unlike some species, H. tengah does not require seasonal variation – stable warm conditions year-round are ideal.
Borneo Halfbeak Diet and Feeding
Feeding H. tengah is easier than often reported – provided you understand one key rule:
If it sinks, it it often ignored.
These fish feed exclusively at the surface until they are well acclimatised to life in aquariums. At which point they may drop an inch or two from the surface to gather foods they missed.
Accepted foods:
- Floating flakes and small granules (once settled or captive bred)
- Buoyant frozen foods like white mosquito larvae are perfect, but other small options like Daphnia are also suitable
- Live foods including baby brine shrimp (Artemia sp.) are great for acclimatising new imports
Anything that drops more than a few inches below the surface will typically be ignored.
Tank Mates for Hemirhamphodon
Choosing tank mates is challenging due to several constraints:
Avoid:
- Boisterous feeders as they can cause food to sink too quickly
- Very small fish as they are at risk being eaten
Ideal tank mates:
Look to species that share the same habitat and temperament:
- Parosphromenus spp. (liquorice gouramis)
- Sphaerichthys spp. (chocolate gouramis)
- Larger Boraras spp. (ensure fully grown)
- Larger Sundadanio spp. (ensure fully grown)
- Wild Betta spp.
- Trigonostigma spp.
The six-banded barb (Desmopuntius hexazona) can work, though it is slightly more active – ensure the halfbeaks are well established first.
Discovering A Family Oddball
I began planning a new tank almost half a year before I could actually get it filled with water. This gave me far too much time to dive into rabbit holes online, researching different habitats to inspire myself. My criteria were straightforward: to utilise botanicals and live plants in combination to produce something aesthetically pleasing, but that combination also had to function like something in nature.
While researching Borneo biotopes, where Cryptocoryne and Bucephalandra grow wild and leaf litter dominates, I discovered that there were more species of halfbeaks than I ever knew existed. Furthermore, all of the species located in the three genera (Hemirhamphodon, Dermogenys, and Nomorhamphus), found within the family Zenarchopteridae, are viviparous.
In viviparous fish, or livebearers as many of us will know them, embryos develop within the female and fully formed fry are birthed (just like the livebearers in Poeciliidae – the guppies, platies, mollies, and more). But there’s one exception – the Borneo redline halfbeak (Hemirhamphodon tengah).
A developing halfbeak embryo
Despite Borneo redline halfbeaks not giving birth to live young, it has been observed that the eggs laid by the females are already fertilised when released. The stage of development at the point of release is still unknown as no consistency to the eggs collected have been recorded.
Interestingly, it is also thought that the sperm transferred to the female during copulation is not immediately used for fertilisation, with the female starting to swell with eggs many days after the event – which could contribute to why there is no consistency to the stage of the eggs upon released.
A study analysing the distribution of life history traits within Zenarchopteridae suggests that the viviparity prevalent across the three genera comes from one common ancestor. Yet an important question remains unanswered. Has H. tengah managed to retain a primitive trait whilst evolving alongside the rest of the genus, or has the species evolved back from live bearing to oviparity?
In my rather uneducated opinion, it is more likely that each of the three genera diverged from the shared ancestor, before the descendants of this ancestor split into the species that we see today. This seems somewhat more plausible than H. tengah splitting off before evolving viviparity, yet developing the same traits as the rest of the Hemirhamphodon species.
Either way, the benefits for this one species not to carry their eggs for the duration of incubation, and the environmental pressures that may have brought it about, remain unclear.
Newly hatched Borneo halfbeak fry
Eggs, Not Babies
The courtship of H. tengah is well detailed by Dorn and Greven, and my experiece in captivity very much aligns with this study.
Initially, a male defends a territory at the surface and when a female is attracted, he will perform a courtship dance moving from the left of the female to the right and back again, always staying behind or next to her. With some beating of the male’s anal fin against the female, sperm is transferred to the genital pore which can be stored for an unspecified time prior to fertilisation.
The female will deposit the eggs in a safe area, typically in dense plant growths near the surface. I have found eggs amongst stems of Limnophila sessiliflora, the roots of water lettuce (Pistia stratiotes) and in woollen spawning mops.
The eggs are almost invisible when first laid
The eggs seem to hatch around the 18th day when maintained at 25°C (77°F). They appear to still have a yolk sac for a couple more days before beginning to feed.
I had success raising them on vinegar eels as a first food, as they tend to swim up to the meniscus of the water – where the babies hunt. I did not record the exact timeline of the progression of their growth, but I soon introduced small powered foods, freshwater copepods and young Daphnia. The youngsters grew steadily and are now fully mature adults themselves.
Borneo Redline Halfbeak Fact File
Scientific name: Hemirhamphodon tengah
Size: To 5cm (2")
Origin: Southern Borneo
Habitat: Densely vegetated blackwater peat swamps
Tank size: 90x30x30cm (36x12x12")
Water requirements: Soft and acidic water; aim for 5.5-6.5pH, 0-8°H
Temperature: 25-28°C (77-82°F)
Temperament: Peaceful but nervous species, not for a general community
Feeding: Strictly takes floating foods, consider frozen white mosquito larvae and small insects as well as flakes and slow sinking granules.
Availability and cost: Rare to find in shops but available from specialist retailers, starting from around £7 each.